PSI - Issue 47

Jesús Toribio / Procedia Structural Integrity 47 (2023) 959–964 Jesús Toribio / Procedia Structural Integrity 00 (2023) 000–000

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4. Pearlite microstructure changes during cold drawing The pearlite microstructural changes during cold drawing (at the two levels of pearlitic colonies and lamellae) were studied by Toribio and Ovejero (1997, 1998a, 1998b, 1998c), showing the following trends: (i) slenderizing of the colonies (Toribio and Ovejero, 1997); (ii) decrease of interlamellar spacing (Toribio and Ovejero, 1998a); (iii) orientation in the direction of cold drawing (wire axis) of both the colonies (Toribio and Ovejero, 1998b) and the lamellae (Toribio and Ovejero, 1998c). This evolution is shown in Fig. 2 for different drawing degrees.

Fig. 2. Microstructures of the hot rolled bar (left) and the cold drawn wire (right) in longitudinal sections. Vertical side of the micrograph is always parallel to the wire axis or drawing direction, whereas horizontal side is associated with the radial direction of the cylinders. 5. Consequences of cold drawing on crack paths Fig. 3 shows the evolution of crack paths with cold drawing under HAC conditions, where a progressive change in the macroscopic topography as the cold drawing increases was observed in all fracture surfaces. For the most heavily drawn steels (4 to 6) the crack deflection takes place suddenly after the fatigue precrack and the deviation angle is close to 90º (propagation step or perpendicular deflection/deviation).

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Fig. 3. Evolution of hydrogen-assisted crack paths (HACP): (a) general appearance of the fracture surfaces; (b) geometric parameters describing the HACP; (c) evolution of fracture profiles; f: fatigue crack growth; I: mode I cracking; II: mixed mode cracking; F: final fracture by cleavage. .